Snails, Snails & More Snails! Members in the group:
Jessica Lau (Secretary)
Daniel Considine
Alfie Gleeson
Sung-joo Song
Jevgenija Petrova
Nikita Vasistha
Introduction
In this experiment we plan to investigate the shell colour polymorphism in Cepaea nemoralis snail, also known either as the brown lip or grove snail. We will do this by obtaining evidence for action of genetic drift, gene flow and selection on the frequency of Cepaea nemoralis shell colour; to attempt to directly correlate our findings with the Cepaea nemoralis’ shell colour polymorphism.
The term polymorphism is when there are two or more clear distinguishable phenotypes existing in the same habitat and time, within the same population of a species. For such happening to occur,the population must be in panmixia.
Why we will study these snails?
Cepaea nemoralis, land snails are extremely prevalent in Western Europe and are famous for their polymorphism, large size and brightly coloured shells. They make ideal study specimens in studying genetics within a population for several reasons. Their coloured shells and slow mobility make them relatively easy to spot and count within the field. Since they will not move too far within a lifetime, they also give a good representation on the genetics within that specific area. Furthermore, with a lifespan of 5-7 years and breeding 1-2 times per year between the months of April to October, Cepaea nemoralis, provides us with ideal information over the genetics of an area over generations.
Last but not least, as we are studying whether there is any reason for polymorphism within Cepaea nemoralis, it is useful that we can identify the mortality factors which may influence survival e.g. biotic (bird predation); abiotic (temperature, altitude).
What we hope to learn from our sampling:
Our sampling will allow us to clearly distinguish whether it is the effect of sampling variation, genetic drift & natural selection or genetic drift alone that accounts for the different allele frequencies within the different localities.
In particular, we are examining shell colour polymorphism in Cepaea nemoralis. Sampling at different locations (all of which are exposed to divergent selection pressures) within the field, will consequently resolve which of the above effects have made the resultant snail populations polymorphic. On a deeper level, seeing polymorphism in action and understanding the basis of this, will allow us to develop our understanding of evolutionary genetics in general.
Our sampling method:
(Please refer to our sampling diagram below....) The sampling was carried out at 6 equally spaced areas crossing a cline to achieve a broad selection of samples in different but adjacent habitats. The sampling areas were spaced apart to try to minimise pseudoreplication, allowing us to establish if true replication is occurring across the cline. A sample of 30 snails was collected from each area to create a sample big enough to be valid and allow statistical testing.
Diagram:
What sort of observation would support your hypothesis, & what would not
Our hypothesis is the shell colour polymorphism in Cepaea nemoralis has a direct link with genetic drift, gene flow or selection within the population itself. Thus we can directly link why shell colour polymorphism in Cepaea nemoralis occurs.
The main observation that would support our hypothesis is the phenotypic variation in the shell colour of the snails found on different sites of the field. The phenotypic and hence the genetic differentiation can be a direct result of evolutionary processes such as genetic drift, selection and gene flow. We believe that the population would experience different selection pressures in different parts of the field and expect a significant allelic divergence because small populations are very susceptible to the random allele fluctuations due to chance. If we do not see any significant differences within the snail population throughout the field, we won’t be able to support our hypothesis.
Members in the group:
Introduction
In this experiment we plan to investigate the shell colour polymorphism in Cepaea nemoralis snail, also known either as the brown lip or grove snail. We will do this by obtaining evidence for action of genetic drift, gene flow and selection on the frequency of Cepaea nemoralis shell colour; to attempt to directly correlate our findings with the Cepaea nemoralis’ shell colour polymorphism.
The term polymorphism is when there are two or more clear distinguishable phenotypes existing in the same habitat and time, within the same population of a species. For such happening to occur,the population must be in panmixia.
Why we will study these snails?
Cepaea nemoralis, land snails are extremely prevalent in Western Europe and are famous for their polymorphism, large size and brightly coloured shells.
They make ideal study specimens in studying genetics within a population for several reasons. Their coloured shells and slow mobility make them relatively easy to spot and count within the field. Since they will not move too far within a lifetime, they also give a good representation on the genetics within that specific area. Furthermore, with a lifespan of 5-7 years and breeding 1-2 times per year between the months of April to October, Cepaea nemoralis, provides us with ideal information over the genetics of an area over generations.
Last but not least, as we are studying whether there is any reason for polymorphism within Cepaea nemoralis, it is useful that we can identify the mortality factors which may influence survival e.g. biotic (bird predation); abiotic (temperature, altitude).
What we hope to learn from our sampling:
Our sampling will allow us to clearly distinguish whether it is the effect of sampling variation, genetic drift & natural selection or genetic drift alone that accounts for the different allele frequencies within the different localities.
In particular, we are examining shell colour polymorphism in Cepaea nemoralis. Sampling at different locations (all of which are exposed to divergent selection pressures) within the field, will consequently resolve which of the above effects have made the resultant snail populations polymorphic.
On a deeper level, seeing polymorphism in action and understanding the basis of this, will allow us to develop our understanding of evolutionary genetics in general.
Our sampling method:
(Please refer to our sampling diagram below....)
The sampling was carried out at 6 equally spaced areas crossing a cline to achieve a broad selection of samples in different but adjacent habitats. The sampling areas were spaced apart to try to minimise pseudoreplication, allowing us to establish if true replication is occurring across the cline. A sample of 30 snails was collected from each area to create a sample big enough to be valid and allow statistical testing.
Diagram:
What sort of observation would support your hypothesis, & what would not
Our hypothesis is the shell colour polymorphism in Cepaea nemoralis has a direct link with genetic drift, gene flow or selection within the population itself. Thus we can directly link why shell colour polymorphism in Cepaea nemoralis occurs.
The main observation that would support our hypothesis is the phenotypic variation in the shell colour of the snails found on different sites of the field. The phenotypic and hence the genetic differentiation can be a direct result of evolutionary processes such as genetic drift, selection and gene flow. We believe that the population would experience different selection pressures in different parts of the field and expect a significant allelic divergence because small populations are very susceptible to the random allele fluctuations due to chance. If we do not see any significant differences within the snail population throughout the field, we won’t be able to support our hypothesis.